The United States ambassador to Denmark barred an American NATO expert critical of President Trump from speaking at an international conference hosted by the American embassy and a Danish think tank, prompting the event’s cancellation, organizers said.
The expert, Stanley R. Sloan, was scheduled to give a keynote speech at the conference, which was celebrating the 70th anniversary of NATO, on Tuesday.
Mr. Sloan, a visiting scholar at Middlebury College in Vermont, a fellow at the Atlantic Council and a former analyst for the Central Intelligence Agency, planned to speak about the future of trans-Atlantic relations.
One day before he was set to leave for Copenhagen, Mr. Sloan was informed that the United States Embassy in Copenhagen had vetoed his participation because of his previous criticisms of President Trump, Mr. Sloan said on Facebook on Saturday.
Carla Sands, the United States ambassador to Denmark, did not want Mr. Sloan to participate, and the Danish Atlantic Council “had no other option” than to revoke his invitation to speak, Lars Bangert Struwe, the secretary general of the council, said in a statement.
Mr. Sloan said the decision had left him “stunned and concerned about our country.”
On Sunday morning, Mr. Struwe canceled the NATO conference.
“After serious consideration, we have decided not to proceed with the conference,” he said on Twitter. “The progress of the process has become too problematic; and therefore, we cannot participate in the conference, let alone ask our speakers to participate.”
From a Danish point of view, the decision to bar Mr. Sloan would turn the conference’s focus to internal American politics and away from the future of NATO, Mr. Struwe said in an interview on Sunday. There were 12 people scheduled to speak, and about 100 attendees were expected, he said.
“We have all the time known that Mr. Sloan has a critical approach towards President Donald Trump,” Mr. Struwe said in the statement. “That is no secret, especially when following his Twitter and Facebook profile. We have, however, never doubted that Mr. Sloan at our conference would deliver an unpolitical and objective lecture.”
In his book, “Defense of the West,” published in 2016, Mr. Sloan discussed the impact that the Trump administration could have on the deterioration of trans-Atlantic relations, given its questionable support for NATO, its relationship with Russia and its response to threats from the Islamic State.
The United States Embassy in Denmark in a series of tweets on Sunday said Mr. Sloan had been added to the program at the last minute — without the same joint decision-making used in recruiting the other speakers.
The event’s cancellation was “unfortunate,” the embassy said, as it would have provided speakers and attendees an opportunity to exchange views and strengthen NATO for the future.
Mr. Sloan posted the speech he had prepared for the conference on Facebook, in which he thanked Ms. Sands for her expression of support for the democratic values that the alliance promotes.
Ms. Sands, who previously worked in the entrepreneurial, investment and philanthropic sectors, was confirmed by the Senate in 2017, according to the embassy’s website. She also served as a board member of several arts and education institutions in California and has a doctor of chiropractic degree from Life Chiropractic College, now Life University, in Marietta, Ga.